The present invention relates to a new silicon rubber mixture, its use for embolization as well as a therapeutic set containing the said mixture. The new mixture and the therapeutic equipment can be used for the first time in the cerebrovascular surgery and general surgery, respectively, for surgical embolization by the aid of a catheter.
Due to their localization or size certain parts of the human arterial system cannot be reached either via direct surgical exposure or endovascular approach, i.e. by means of the generally used rigid "Seldinger type" catheters (secondary and tertiary arteries). This problem has been solved by the use of balloon catheters of a diameter less than 1 mm. These flexible catheters are provided with an inflatable natural rubber balloon head, which can utilize the so-called "parachute-effect" of the blood stream. These balloon-catheters have particular importance for the cerebral endovascular surgery.
The cerebral arteries are surrounded by a stiff bony wall on the cranial base and have "syphons". Thus, the intracranial arteries become available only by using such catheters. The microcatheter filled with X-ray contrast medium, measurable by means of fluoroscopic screen, gives the possibility to follow exactly the position of the balloon-head. When using two or special balloon catheters at the same time, the catheter can also be directed into the secondary arteries. However, the above method is of diagnostic importance only, because the catheter when sent to its destination is left for blocking, it will also block the functionally important main vessels due to secondary thrombosis. This complication can be eliminated if the balloon were left in the vessels isolated, by detaching and withdrawing the catheter. The isolation and the so-called "superselective" embolization is ensured by the physical possibility that the inflated balloon head which is fixed to the inner wall of the vessel to be blocked is stronger than the flexible connection between the balloon and the ending of the catheter. However, the detachment of the balloon head, filled with fluid, is dangerous on the one hand, as the balloon can leave its place; on the other hand it can be unsuccessful when the fluid flows out of the balloon. Filling a quickly hardening fluid in the catheter ensures the stable fixing of the balloon in the vessel and a permanent, safe occlusion of the desired area.
The object of the present invention is to provide a novel and useful therapeutic equipment by which the above detachment and thus the embolization of certain vessels and permanent blocking of further ducts, respectively, can be performed easily and with great certainty without any problems at imparting the catheter.
The above balloon catheter method has been theoretically worked out recently by F. Sorbinenko [J. of Neurosurgery 41, 125-145 (1974)]. No material has been found, however, which allowed that the catheter could be detached effectively. Moreover, in the absence of the contrast material the position of the catheter could not be followed.
P. Schaps in Zentralblatt fur Neurochirurgie 38, 105-10 (1977) describes the use of silicon together with a microcatheter and a balloon. However, the viscosity of the material used was so high that only ice-cooling technique could be applied. Moreover, this material contained no X-ray contrast material.
G. Debrun, P. Lacour, J. Caron et al. [J. of Neurosurgery 49, 635-49 (1978) ] describe similar methods. They report, however, difficulties with the impartation. In operations, detachment could be performed by using a coaxial catheter and thus, the technique could not be used with safety for the intracranial vascular free operations.
S. K. Hilal, P. Sane, W. J. Michelson and A. Kossein, Neuroradiology 16, 430-33 (1978) describe the use of silicon elastomer (Silastic 382), methyl silicon oil and tantalum powder in the microcatheter technique. The disadvantage of said mixture was the much higher viscosity than was good for an easy injection, and on the other hand the use of tantalum powder, as X-ray contrast material obstructed the catheter by forming plugs. Moreover, the tantalum powder is toxic.
In summary, there was no material available which corresponded to all the requirements as discussed above. These requirements are as follows:
1. The low viscosity is very important: the material should be pressed through a catheter of 0.1 mm. inner diameter and 150 mm. length. This requirement is very hard to provide, considering that the fluid injected should harden within a short period.
2. Due to the limited time for operations, the material should harden within a short time (i.e. 10 to 20 min.) so that sufficient time to inject the mixture (min. 3 to 4 min.) should also be provided.
3. The material should evenly fill in the catheter with sufficient plasticity so that no bubble is allowed to occur.
4. After hardening, however, the material should be rigid to a certain extent, i.e. it should break at the detachment point.
5. It is very important for the precise dosing and control that the material should also give X-ray shadow. This characteristic provides that the position of the catheter and balloon, respectively, can be followed.
6. Sterility, no toxic effect.